I asked a very similar question not long ago while I was making my decision. The only reason I considered the MagnaFlows was because I didn't want my car to be too too loud, but I wanted a nice deep tone to reflect some of my mods I've made (past and future).
Well, I went AGAINST the Muffler shops advice (With some thanx to InitialDGP) And let me tell you Im thrilled with my FlowMasters.
I Went with the Delta 50's and they are exactly what I wanted. Nice and Deep, Not too loud.
Also, something worth spouting about was I got a free upgrade! From what to what i'm not sure, but the Muffler Shop guy showed me a sticker that came in the box saying "Congratulations, We've upgraded your XXX to XXX for free" etc... I was in a big rush to not show the wife the bill so I missed the finer details
I'll try to shoot some Video in and out of the car that you can compare agains Herc's video to get a feel for the diff between the 50's and 40's to help with your decision if you go with FlowMasters.
Cheers!